Endothelin-1 stimulates deoxyribonucleic acid synthesis and contraction in testicular peritubular myoid cells

ATP activation of peritubular cells drives testicular sperm transport

Spermatogenesis, the complex process of male germ cell proliferation, differentiation, and maturation, is the basis of male fertility. In the seminiferous tubules of the testes, spermatozoa are constantly generated from spermatogonial stem cells through a stereotyped sequence of mitotic and meiotic divisions. The basic physiological principles, however, that control both maturation and luminal transport of the still immotile spermatozoa within the seminiferous tubules remain poorly, if at all, defined. Here, we show that coordinated contractions of smooth muscle-like testicular peritubular cells provide the propulsive force for luminal sperm transport toward the rete testis. Using a mouse model for in vivo imaging, we describe and quantify spontaneous tubular contractions and show a causal relationship between peritubular Ca2+ waves and peristaltic transport. Moreover, we identify P2 receptor-dependent purinergic signaling pathways as physiological triggers of tubular contractions both in vitro and in vivo. When challenged with extracellular ATP, transport of luminal content inside the seminiferous tubules displays stage-dependent directionality. We thus suggest that paracrine purinergic signaling coordinates peristaltic recurrent contractions of the mouse seminiferous tubules to propel immotile spermatozoa to the rete testis.

Morphologic manifestations of testicular and epididymal toxicity

Histopathologic examination of the testis is the most sensitive means to detect effects on spermatogenesis; however, the complexity of testicular histology, interrelatedness of cell types within the testis, and long duration of spermatogenesis can make assessment of a testicular toxicant challenging. A thorough understanding of the histology and morphologic manifestations of response to injury is critical to successfully identify a testicular effect and to begin to understand the underlying mechanism of action. The basic patterns of response to xenobiotic-induced injury to the testis and epididymis are detailed and discussed.

Angiotensin II regulates testicular peritubular cell function via AT1 receptor: a specific situation in male infertility

We observed that peritubular myoid cells in the human testis are immunoreactive for angiotensin II (AngII) receptors (AT1R) and explored AngII actions in cultured human testicular peritubular cells (HTPCs). In response to AngII they contracted within minutes. The AT1R-blocker losartan blocked contraction, implying involvement of AngII and AT1R in intratesticular sperm transport. AngII also significantly increased IL-6 mRNA levels and IL-6 secretion within hours and losartan again prevented this action. This suggests involvement in inflammatory processes, which may play a role in male infertility. AngII can be generated locally by mast cell (MC)-derived chymase (CHY), which cleaves AngI. In testicular biopsies from infertile men we found abundant MCs, which express CHY, within the wall of seminiferous tubules. In contrast, CHY-positive MCs are hardly found in normal human testis. Testicular inflammatory events may fuel processes resulting in impaired spermatogenesis. Therefore therapeutic interference with MCs, CHY or AT1R might be novel options in male infertility.

Role of angiotensin and endothelin in testicular ischemia reperfusion injury

OBJECTIVES

To determine whether angiotensin and endothelin have any role in testicular ischemia reperfusion injury by investigating the effects of the angiotensin converting enzyme inhibitor enalapril, selective non-peptide angiotensin-II type I blocker losartan and dual endothelin receptor blocker bosentan.

METHODS

Rats were anesthetized with thiopental sodium (50 mg/kg i.p.) before the operation. The left testicular artery and vein of rats were occluded for 1 h; before the bilateral orchiectomy, the organ was allowed to reperfuse for 3 h or 24 h. Enalapril (20 mg/kg i.p.), losartan (30 mg/kg i.p.), bosentan (10 mg/kg i.p.) or vehicle (saline) were given 30 min before reperfusion. Malondialdehyde level was measured in testicular tissue after 3 h of reperfusion. Histological examination was carried out after 24 h of reperfusion.

RESULTS

Ischemia reperfusion caused a significant increase in malondialdehyde level of ipsilateral testis, and histopathological injury in both ipsilateral and contralateral testes. Enalapril, losartan and bosentan treatments prevented the ischemia reperfusion-induced augmentation in malondialdehyde levels. Only bosentan treatment ameloriated ischemia reperfusion-induced histopathological alterations.

CONCLUSIONS

Endothelin might play a more important role in pathogenesis of testicular ischemia reperfusion injury when compared with angiotensin.

Identification and characterization of Myosin from rat testicular peritubular myoid cells

In the mammalian testis, peritubular myoid cells (PMCs) surround seminiferous tubules. These cells are contractile, express the cytoskeletal markers of true smooth muscle-alpha-isoactin and F-actin-and participate in the contraction of seminiferous tubules during the transport of spermatozoa and testicular fluid to the rete testis. Myosin from PMCs (PMC-myosin) was isolated from adult rat testis and purified by cycles of assembly-disassembly and sucrose gradient centrifugation. PMC-myosin was recognized by a monoclonal anti-smooth muscle myosin antibody, and the peptide sequence shared partial homology with rat smooth muscle myosin-II, MYH11 (also known as SMM-II). Most PMC-myosin (95%) was soluble in the PMC cytosol, and purified PMC-myosin did not assemble into filaments in the in vitro salt dialysis assay at 4 degrees C, but did at 20 degrees C. PMC-myosin filaments are stable to ionic strength to the same degree as gizzard MYH11 filaments, but PMC-myosin filaments were more unstable in the presence of ATP. When PMCs were induced to contract by endothelin 1, a fraction of the PMC-myosin was found to be involved in the contraction. From these results we infer that PMCs express an isoform of smooth muscle myosin-II that is characterized by solubility at physiological ionic strength, a requirement for high temperature to assemble into filaments in vitro, and instability at low ATP concentrations. PMC-myosin is part of the PMC contraction apparatus when PMCs are stimulated with endothelin 1.

Exploring human testicular peritubular cells: identification of secretory products and regulation by tumor necrosis factor-alpha

Testicular peritubular cells are myofibroblastic cells, which represent the major cellular components of the wall of the seminiferous tubules. In men their phenotypic characteristics, including possible secretory activity and regulation, are not well known, in neither normal nor pathologically altered testes. Especially in testes of men with impaired spermatogenesis, the cytoarchitecture of the tubular wall is frequently remodeled and presents fibrotic thickening, increased innervation, and infiltration by macrophages and mast cells. The latter are two sources of TNF-alpha. The purpose of our study was to explore human testicular peritubular cells and mechanisms of their regulation. To this end we primarily studied cultured human testicular peritubular cells (HTPCs), isolated from adult human testes. Having established that HTPCs express TNF-alpha receptors 1 and 2 and respond to recombinant human TNF-alpha by a rapid phosphorylation of ERK1/2, we used complementary approaches, including gene array/RT-PCR studies, Western blotting/immunocytochemistry, and ELISA techniques to study phenotypic characteristics of HTPCs and actions of TNFalpha. We found that HTPCs express the nerve growth factor gene and TNF-alpha-stimulated mRNA levels and secretion of nerve growth factor in a dose- and time-dependent manner. Similarly, monocyte chemoattractant protein-1 was identified as a product of HTPCs, which was regulated by TNF-alpha in a concentration- and time-dependent manner. TNF-alpha furthermore strongly enhanced expression and/or synthesis of other inflammatory molecules, namely IL-6 and cyclooxygenase-2. Active cyclooxygenase-2 is indicated by increased prostaglandin D2 levels. In addition, intercellular adhesion molecule-1, which was not detected at protein level in the absence of TNF-alpha, was induced upon TNF-alpha stimulation. In conclusion, these results provide novel insights into the nature of human peritubular cells, which are able to secrete potent signaling molecules and are regulated by TNF-alpha. These results also hint to an as-yet-unknown role of peritubular cells in normal human testis and involvement in the pathomechanisms associated with impaired spermatogenesis in men.

Strontium fructose 1,6-diphosphate rescues adenine-induced male hypogonadism and upregulates the testicular endothelin-1 system

1. Male hypogonadism is a major problem that starts to affect middle-aged men and has adversely effects on human sexual life. The aim of the present study was to investigate the effect of strontium fructose 1,6-diphosphate (FDP-Sr) on male hypogonadism in rats. 2. The pharmacological model of testis dysfunction was created by administration of adenine (200 mg/kg per day, i.g.) for 30 days. Three doses of FDP-Srs (200, 100 and 50 mg/kg per day, i.g.) were administered in parallel with adenine. Finally, mating behaviour index (the mounting latency and the number of mounting events), the total number of spermatozoa and sperm motility, related enzyme function and gene regulation and the mRNA levels of steroidogenic acute regulatory protein (StAR), cytochrome P450 side-chain cleavage enzyme (P450scc), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), prepro-endothelin (ET)-1, endothelin-converting enzyme (ECE) and endothelin receptor A (ET(A)) were analysed. 3. The results showed that adenine significantly prolonged the mounting latency and decreased the number of mounting events, markedly reduced the total number of spermatozoa, slowed sperm motility and decreased testicular enzyme activity in the testes. At the mRNA level, adenine significantly downregulated serum testosterone, StAR, P450sc and 3beta-HSD. In parallel, adenine also targeted the ET-1 system, significantly downregulating mRNA levels of prepro-ET-1, ECE and ET(A). Administration of FDP-Sr dose-dependently reversed these effects. 4. In conclusion, adenine-induced testis dysfunction appears to be manifested as loss of sexual function in association with decreased spermatogenesis and reduced mRNA levels of steroidogenesis and the testicular ET-1 system. These abnormalities were significantly restored by FDP-Sr in a dose-dependent manner. These data indicate the possibility of using FDP-Sr to treat male hypogonadism.

Ghrelin inhibits angiotensin II-induced migration of human aortic endothelial cells

Ghrelin, the endogenous ligand for the GH secretagogue receptor, is produced by the oxyntic cells of the stomach and is involved in the regulation of energy balance. However, an increasing number of direct ghrelin cardiovascular effects, and, among them, high ghrelin binding in atherosclerotic coronary arteries, are being reported. We investigated whether ghrelin affects migration of human aorta endothelial cells (HAEC). HAEC bound ghrelin in specific, saturable manner. Ghrelin, as such, did not affect HAEC migration, however it inhibited the angiotensin II-induced migration, and this effect was inhibited by the antagonist (D-Lys(3))-GHRP-6. In HAEC, ghrelin elicited increased intracellular concentration of cAMP that was involved in its effect on AngII-induced HAEC migration, as the AMP cyclase inhibitor SQ22.536 and PKA inhibitor KT5720, respectively, inhibited and blunted it. These findings suggest a role of ghrelin in the control of endothelial cell migration and its possible involvement in vascular changes present in disorders characterized by low plasma ghrelin.

Phorbol myristate acetate induces changes on F-actin and vinculin content in immature rat Sertoli cells

Actin and vinculin are two of the most abundant cytoskeletal proteins, widely expressed in nearly all types of eukaryotic cells. It has been well established that long-term exposure to the tumor promoter phorbol myristate acetate (PMA) affects Sertoli cell morphology, as well as F-actin and vinculin organization in vitro. To analyze in a quantitative manner the F-actin and vinculin content of rat immature Sertoli cells in vitro in response to PMA exposure, cytoskeletal fractions were prepared following extraction with Triton X-100. Analysis of the isolated cytoskeletal fractions by immunoblotting showed that exposure of immature rat Sertoli cells to PMA for 8h has an appreciable effect on the cellular level of both the actin and vinculin. Interestingly, as revealed by using calphostin C, a specific protein kinase C inhibitor, the observed F-actin and vinculin changes are most probably mediated by a mechanism that depends on protein kinase activity. A discussion is made concerning PKC modulation by PMA and the subsequent actin and vinculin quantitative changes and reorganization, phenomena that have been closely related to cell transformation.

Bradykinin increases intracellular calcium levels in rat testis peritubular cells via the B2 receptor subtype

1. RT-PCR and Western blots were used to detect bradykinin B(2) receptors in testis and isolated peritubular cells of pre-pubertal rats. RT-PCR demonstrated expression of a single transcript, whereas Western blots showed up to three specific bands that were in accordance with the described native, glycosylated and dimeric form of B(2) receptor proteins, respectively. 2. Fura-2-loaded peritubular cells responded with an instantaneous, linear and transient rise in [Ca(2+)](i) after adding bradykinin. Stimulation of cells with bradykinin concentrations between 1 micro M and 1 pM showed a dose dependent increase of [Ca(2+)](i). The calcium response to bradykinin was diminished after stimulation of peritubular cells in calcium-free buffer. After blocking the SERCA-pumps by thapsigargin and subsequent stimulation with bradykinin, no rise of [Ca(2+)](i) was appreciated. 3. Multiple stimulation of a single peritubular cell by local perfusion with a brief addition of BK (10 nM) resulted in a fast and immediate response. However, the second and third stimuli had slower rise rates and diminished [Ca(2+)](i) peaks, showing desensitization of the kinin receptor. 4. Addition of the bradykinin B(1) receptor agonist [des-Arg(9)]-bradykinin (100 nM) to Fura-2-loaded peritubular cells did not change the [Ca(2+)](i). However, the B(2) receptor antagonist HOE 140 (100 nM) strongly inhibited the bradykinin-induced calcium response. 5. We conclude that the bradykinin-induced increase in [Ca(2+)](i), in testicular peritubular cells is mediated by the stimulation of kinin receptors of the B(2) subtype.

Erythropoietin expression in primary rat Sertoli and peritubular myoid cells

Kidney and liver are the major organs of erythropoietin (Epo) synthesis. However, Epo messenger RNA (mRNA) has been detected in several organs, such as brain, lung, and testis. Furthermore, functional Epo receptors have been demonstrated on different cell types, including rat Leydig cells. The aim of the study was to identify testicular cells expressing Epo mRNA and to quantitate its levels by competitive reverse transcriptase-polymerase chain reaction (RT-PCR). Besides whole testis, Epo transcripts were found in Sertoli and peritubular myoid cells, while no signal was detected in Leydig cells. Exposure of Sertoli cells to CoCl(2) led to an increase of Epo mRNA level. Semiquantitative competitive RT-PCR presented an increase in the level of Epo mRNA in Sertoli cells stimulated by follicle-stimulating hormone, while exposure of peritubular myoid cells cultures to testosterone reduced Epo mRNA expression. Due to the blood-testis barrier, basal expression of Epo suggests a not yet defined function of this hormone in testis.

Adrenomedullin inhibits the contraction of cultured rat testicular peritubular myoid cells induced by endothelin-1

The present study documents that adrenomedullin (AM), a vasoactive peptide originally identified in pheochromocytoma tissue and present in the testis, in vitro affects the function of testicular peritubular myoid cells (TPMC), a contractile cell type located in the seminiferous tubule wall. AM stimulated cAMP production by cultured TPMC taken from 16-day-old rats, and this effect was completely inhibited by the AM antagonist AM-(22-52) and partially by the CGRP (calcitonin gene-related peptide) antagonist CGRP-(8-37). Studies on TPMC contractile activity documented that AM inhibits TPMC contraction induced by endothelin-1 (ET-1) and that its effect is antagonized by AM-(22-52). Neutralizing AM produced by TPMC with the addition of anti-AM antibody induced a significant increase of ET-1-induced contraction. When exposed to the protein kinase A inhibitor H-89, AM inhibitory activity on ET-1-induced TPMC contraction was suppressed, whereas the nitric oxide synthase inhibitor N:(G)-nitro-L-arginine methyl esther did not modify AM activity. In conclusion, our study indicates that AM stimulates cAMP production and inhibits the contraction induced by ET-1 in TPMC in vitro, and that AM produced by TPMC has an autocrine effect. We propose that AM may have a role in the control of seminiferous tubule contraction.

Follicle-stimulating hormone, testosterone, and hypoxia differentially regulate UDP-glucuronosyltransferase 1 isoforms expression in rat sertoli and peritubular myoid cells

Uridine diphosphoglucuronosyltransferases (UGTs) are detoxifying enzymes responsible for the metabolism of endogenous and xenobiotics compounds. UGT isoforms are widely distributed in rat tissues showing a constitutive and inducible gene expression. However, little information is available concerning UGTs expression in testis. The UGT1A1, UGT1A2, and UGT1B1 mRNAs expression in whole rat testis, in Sertoli and peritubular myoid cells in basal conditions, and after hormonal and hypoxic stimulation were investigated by reverse transcriptase-polymerase chain reaction (RT-PCR). Constitutive expression of each UGT1 isoform was present in rat testis with higher levels of UGT1A2. UGT transcripts were also detected in Sertoli and peritubular myoid cells. After FSH stimulation, Sertoli cells showed an increase in UGT1B1 mRNA expression, whereas the levels of UGT1A1 and UGT1A2 resulted unmodified. The main effect induced by testosterone was a decrease of UGT1B1 mRNA expression in peritubular myoid cells, whereas in Sertoli cells an increase in UGT1A1 and UGT1B1 was observed. In hypoxic conditions, a reduction in UGTs mRNA levels was detected in both cell types. These findings suggest that rat UGT1 isoforms are regulated in testis by hormonal and environmental factors. Thus, it was speculated that alterations in UGTs expression and/or activity may be involved in the pathogenesis of testis injury.

Testicular peritubular myoid cells are a target for adrenomedullin

Adrenomedullin (AM) is a recently cloned vasorelaxing peptide that belongs to the calcitonin gene-related peptide family. AM inhibits the contraction of several types of smooth muscle cells and is present in the testis as well as in many other organs. The authors investigated whether testicular peritubular myoid cells (PMC) possess specific receptors for AM. Binding of AM to PMC was saturable in a time-dependent manner and 125I-AM binding was effectively displaced by cold AM. The study documents that testicular peritubular myoid cells are a target for adrenomedullin and suggests a role for this peptide in the paracrine regulation of the testis.

A novel aspect of lindane testicular toxicity: in vitro effects on peritubular myoid cells

The in vitro effects of the insecticide lindane have been investigated in rat testis peritubular myoid cells (PMCs). Upon PMC exposure to lindane, polarity increase and decrease of dipole dynamics were seen at the membrane level (EC50 20 microM), leading to a partial dissipation of the membrane intrinsic dipole potential. The initial membrane depolarization was increased by Cl- efflux and limited by Ca(2+)-activated repolarizing currents. Concomitantly, lindane produced an increase in [Ca2+]i (EC50 125 microM) resulting from both Ca2+ release from an inositol 1,4,5-trisphosphate-sensitive intracellular store and a voltage-dependent Ca2+ influx from the extracellular medium. Of particular interest from a toxicologic point of view, insecticide concentrations well below those effective in altering ion homeostasis potently inhibited both [Ca2+]i increase and contraction induced by the natural agonists vasopressin and endothelin-1 (IC50s < 10 microM). These data demonstrate that PMCs are highly susceptible to lindane and suggest that the insecticide may exert testicular toxicity by interfering with hormone-regulated PMC function.

Vitamin A modulation of basement membrane production by purified testicular myoid cells

Purified myoid cells, isolated from prepubertal rat testes, cultured in a chemically defined medium for up to 1 week do not change their metabolic activities, evaluated as protein synthesis and secretion, during the culture time. We report that fibronectin, collagen IV, and laminin are synthesized and secreted by myoid cells as demonstrated by immunocytochemical and biochemical methods. The deposition of all three proteins was spotty, with different regional localizations. The effect of vitamin A on the synthesis and the secretion of the basement membrane components was also evaluated. Retinol supplementation induces a higher synthesis of fibronectin and laminin, whereas it does not change collagen IV synthesis and secretion. The secretion of the other two molecules is differentially regulated by retinol; in fact fibronectin secretion is increased, whereas laminin secretion is reduced. Similar results were obtained utilizing retinoic acid. The data we report in this paper show, for the first time, that purified testicular myoid cells synthesize and secrete fibronectin, collagen IV, and laminin and that synthesis and secretion of these components of the basement membrane are regulated by retinol. These findings reveal a new effect of vitamin A in the regulation of mammalian spermatogenesis.

Activation of protein kinase C pathway by phorbol ester results in a proteoglycan synthesis increase in peritubular cells from immature rat testis

In cultured peritubular cells (PT) from rat testis, protein kinase C (PKC) was activated by phorbol 12-myristate 13-acetate (PMA). PMA enhanced the synthesis of proteoglycans (PG) and to a lesser extent their catabolism; the stimulation of the synthesis appeared to be due to an increase in PG protein moiety production and, at the same time, to an increase in the glycanation process as revealed by the use of an exogenous acceptor, p-nitrophenyl-beta-d-xyloside. In the presence of PMA, the molecular weight of neosynthesized PG and the length of their constitutive glycosaminoglycan chains were not modified. Moreover, the distribution of proteochondroitin sulfate and proteoheparan sulfate in medium and in cell layer remained unchanged. However, PMA reduced the sulfation level of chondroitin sulfate and heparan sulfate chains, suggesting that PKC activation resulted in an independent modulation of the sugar chain formation and of the sulfate residue transfer. PMA effect on the synthesis of hyaluronan was also determined: PMA dramatically enhanced its production by PT cells.

Stimulatory action of endothelin-1 on rat Leydig cells: involvement of endothelin-A subtype receptor and phospholipase A2-arachidonate metabolism system

In a previous report we have observed that endothelin-1 (ET-1) is able to stimulate testosterone (T) production by rat Leydig cells revealing an interaction with human chorionic gonadotropin (hCG). The present study was designed to further characterize the stimulatory action of ET on testicular steroidogenesis, to evaluate which subtype of ET receptors is involved in this activity and to examine the role of phospholipase A2 (PLA2)-arachidonate metabolism system in ET-1 transduction mechanism. To this purpose we investigated: i) the interaction of ET-1 with another secretagogue of T, like luteinizing hormone releasing hormone (LHRH); ii) the interference of ET(A) and ET(B) receptor antagonists (BQ-123 and BQ-788, respectively) and of inhibitors of PLA2 (quinacrine) and arachidonate lipoxygenase pathway (nordihydroguaiaretic acid:NDGA) on ET-1-induced T and PGE2 secretion from purified rat Leydig cells. Data obtained indicate that ET-1 amplified T and PGE2 response to LHRH and this secretagogue in turn potentiated testicular steroidogenesis stimulated by endothelin. The ET(A) antagonist, BQ-123, inhibited in a dose-related fashion ET-1-induced T production whereas ET(B) antagonist, BQ-788, failed to affect T response to the peptide. Furthermore, ET(A) antagonist inhibited the stimulatory effect of ET-1 on hCG- or LHRH-induced T secretion and it was able to exert a dose-dependent inhibition of ET-1-stimulated PGE2 output. Moreover, a PLA2 inhibitor quinacrine inhibited the stimulatory action of ET-1 on T production and suppressed basal and ET-1-induced PGE2 release whilst a lipoxygenase blocker NDGA did not modify T response to the peptide. Taken together these findings i) indicate additivity of effects between ET-1 and LHRH in stimulating T and PGE2 production; ii) confirm that ET(A) subtype receptors mediate the stimulatory action of ET-1 on rat Leydig cells; iii) strongly suggest that PLA2-arachidonate metabolism system is involved in endothelin transduction mechanism.